Photographic developing process for producing positive or negative images



Oct. 18, 1966 1. E. THEODOROU 3, 9,

PHOTOGRAPHIC DEVELOPING PROCESS FOR PRODUCING POSITIVE OR NEGATIVE IMAGES Filed Jan. 17, 1963 INVENTOR. IGNATIUS THEODOROII ATTORNEYS United States Patent PHOTOGRAPHIC DEVEiOPING PROCESS FOR PRODUCING POSITIVE 0R NEGATIVE IMAGES Ignatius E. Theodor-on, Watertown, Mass, asslgnor, by

mesne assignments, to Technical Operations, Incorporated, a corporation of Delaware Filed Jan. 17, 1963, Ser. No. 252,171 3 Claims. (Cl. 9663) This invention relates to hotography and more particularly to novel photographic media and processes for using such media to provide visible images. The photographic media of the present invention comprise media of the type formed of a substantially homogeneous mass of contiguous microcrystals of silver halide formed as a binder-free layer upon a suitable support. A process for manufacturing the latter type of media, as by a vacuum evaporation technique, is disclosed in French Patent No. 1,267,623 granted June 21, 1961 to Technical Operations, Incorporated. Media of this latter type can readily be distinguished from other silver halide photographic media, particularly emulsion-type photographic films, not only structurally and by method of manufacture, but for some purposes by the superior acutance, high resolution and quick developability of the binder-free stratum. Such binder-free silver halide media, prepared by evaporation techniques, generally exhibit native sensitivities, in terms of ASA speed, in about the range of 1x to 1X l0" Because the latter type of media are formed of microcrystalline silver halide substantially without a protective binder, such as the gelatin in silver halide emulsions, they are somewhat more susceptible than emulsion-type film to damage from mechanical abrasion or chemical action from airborne pollutants such as hydrogen sulfide or the like. Additionally, because these media have a native ASA speed which is rather low for many purposes, and the spectral response of such media is largely toward the blue end of the spectrum, sensitization to increase both the speed and the panchromaticity of response is obviously desirable. Unfortunately it has been found that when chemical sensitizers to increase speed, and dye sensitizers to enhance spectral response are both applied to the same surface of the silver halide layer, the sensitizing actions generally have been antagonistic to one another.

Also, while efforts have been made to provide photosensitive media and processes for image reproduction including the direct formation of positive images (i.e. images having image densities inversely proportional to the intensity of :the actinic radiation forming such images), none of these efforts has provided media or processes capable of providing from the same medium a direct positive or negative image optionally dependent only upon the choice of two processing techniques, a first of which involves the use of a surface developer under first conditions of ambient radiation during the development process, and a second of which involves the use of a developer under other conditions of ambient radiation during the development process.

One object of the present invention is therefore to provide a novel photographic medium which is simple and economical to make and to use. Another object is to provide a sensitized microcrystalline binder-free silver halide medium which exhibits improved resistance to mechanical or gaseous chemical attack and hence has superior storage qualities. Yet another object of the present invention is to provide such a medium which is both chemically and optically sensitized, and methods and materials for achieving such dual sensitization.

Another important object of the present invention is to provide a novel photographic medium comprising a 3,279,920 Patented Oct. 18, 1966 binder-free microcrystalline silver halide layer, and methods for processing same, following exposure, to selectively obtain either direct positive or negative images depending on the choice between combinations of (l) a condition of ambient radiation at the time of development and (2) whether or not the selected developer is a surface or internal developer.

Other objects of the present invention are to provide a medium of thetype described which includes an organic polymeric layer over the photosensitive stratum thereof, which layer serves to protect said stratum and contributes to the sensitization thereof; to provide a medium of the type described in which the protective layer is compatible with known optical sensitizers; to provide a method for compatibly chemically and optically sensitizing a medium of the type described.

Other objects of the present invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the processes involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the products and compositions possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims. For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein there is shown a dia' grammatic cross-sectional view of one embodiment of this invention.

The above objects are attained in accordance with the present invention which, in one aspect as shown in the drawing comprises a suitable support 20, such as a sheet material, having a subbing layer 22 on one surface thereof. Subbing layer 2 2, in turn, supports a substantially binder-free, homogenous, microcrystalline, photosensitive, thin silver halide layer or stratum 24. Stratum 24 is preferably sandwiched or disposed between subbing layer 22 and a protective speed-enhancing layer 26. Layer 26 comprises an organic polymeric material which is substantially solid (i.e. neither liquid nor viscous but dry to touch), is soluble or permeable in a selected silver halide developer solution or vehicle, and, of course, is substantially transparent to actinic radiation.

The novel processes of the invention in their broader aspects comprise exposing to actinic radiation selected areas of the photosensitive stratum described above, selecting a silver halide developing solution chosen from the group of surface developing solutions (those capable of and intended to develop surface latent images and therefore containing substantially no silver halide solvent) and internal developer solutions (those capable of and in tended to develop internal latent images and therefore preferably containing substantial amounts of silver halide solvent, such as sodium thiosulfate solution), and treating the exposed medium with the selected developer solution while under predetermined conditions of ambient radiation. When the surface developing solution is employed, and treatment of the'exposed medium therewith is effected in the presence of actinic radiation, a positive image will be formed. Alternatively, when either of the internal or surface developing solutions is chosen and the exposed medium is treated therewith in the absence of actinic radiation, a negative image will be formed.

Material suitable for forming support 20 includes papers of all types, such as are used in making photosensitive silver halide emulsion materials, in the form of sheets, films, and plates. Other suitable materials are various insoluble (i.e. in treating or processing solutions such as developer solution) and preferably relatively inert synthetic resins and high molecular Weight polymers. For instance, where it is intended to use a predetermined developer solution which is aqueous, suitable materials for the support include addition polymers, e.-g. polymers of vinyl chloride, vinylidene chloride, vinyl acetate, styrene, isobutylene and acrylonitrile and their copolymers; linear condensation polymers, e.g. polyesters such as polyethylene-terephthalate, polyamides such as polyhexamethylene sebacamide, polyester amides such as polyhexamethylene adipamide/adipate; cellulose derivatives, e.g. cellulose triacetate; vitreous materials such as glass, ceramic or the like, and others.

The support material may be transparent, translucent, or opaque to radiation actinic to the silver halide, and may be used to directly provide a condensation surface, or may be coated optionally with subbing layer 22. The subbing layer may be provided for several purposes, e.g. to alter support opacity, to change support reflectivity, to modify adherence of the microcrystalline binder-free silver halide layer 24 to the support, and for other reasons. Methods and materials for coating such subbing layers on base ma terials are well known and need not be describe-d here.

A microcrystalline binder-free silver halide layer of the present invention may be formed by vacuum evaporation techniques similar to those described in the aforesaid French patent. A basic machine of the kind useful to form such media by vacuum evaporation is illustrated and described in the book Vacuum Deposition of Thin Films by L. Holland published by John Wiley & Sons, NYC, 1948, pp. 7-8. Vacuum coating apparatus of this type is well known and usually comprises an evacua'table container such as a bell jar, and means for evacuating the latter to an ambient pressure which is preferably less than approximately l 10 mm. of Hg. The latter appears to be the maximum pressure at which reasonably desirable layer formation can be achieved. Included within the bell jar is a crucible or boat which is intended to carry the material which is to be evaporated. \Means for heating the boat are usually included, and in one form of the apparatus, the boat is made of tungsten provided with leads to a source of electrical power so that the filament can be heated electrically. By this method the temperature of the evaporating material can be readily controlled. Other methods for heating the star-ting material may also be used, for instance electrical induction. The apparatus also includes means for holding substrate material such as support sheet 20, at a predetermined location within the bell jar wherein preferably one surface of the substrate faces the boat, thus insuring that the stream of vapor from the evaporating material in the boat will strike the substrate surface and condense thereon to form a film or layer according to the well-known principles of evaporation techniques. It is preferred to keep the silver halide layer thus formed as a layer of relatively uniform thickness Within a thickness range of about 0.1 to 0.5 micron (i.e. 03:0.2 micron) inasmuch as optimum photographic parameters such as gamma, density, and speed are found within this range.

In One method of using this apparatus, a quantity of silver halide (e.g. of purity 99.99% or better) is placed within the container, for example, at a first location. A suitable support sheet is placed within the container at a second location displaced from the first location. The container is pumped down to achieve an operating pres sure, and the silver halide is brought to a point above its melting temperature at which evaporation will occur. The resulting vapor is then condensed upon the support surface to form the microcrystalline silver halide layer.

It is preferred that the temperature of the silver halide melt and the pressure of the system be substantially stable during the silver halide deposition operation; for example, when evaporating silver bromide, the temperature may be kept at about 560 C. and the pressure at about lmm. of Hg. A silver halide deposition process,

which can be used to form the silver halide stratum of the medium of the invention, is described in detail in the aforesaid French patent.

Among the silver halides which are useful in evaporation processes to form the microcrystalline binder-free silver halide layer of the present invention, are silver bromide, silver chloride and silver iodobromide. The thickness of the silver halide layer formed from these materials may be readily controlled by adjustment of the evaporation temperature, the evaporation time, and the distance between the silver halide source and the support sheet, or any combination thereof. The layer thus pro vided (which is a thin layer not more than 3.5 microns in thickness and preferably within the range described above) appears to be approximately within 10% of the density of that of a solid macrocrystal of the same silver halide.

The polymers useful as materials, out of which layer 26 can beformed, are those which are film-formers, i.e. materials which can be applied in liquid form either per se, or from a liquid solution, and will, under normal conditions of temperature and pressure, solidify to form a substantially dry coating which is transparent to actinic radiation, preferably visible light. For the purposes of the present invention, suitable polymeric materials are also necessarily permeable or soluble in the developer vehicle. For example, Where the developer solution is aqueous, the useful polymers to form layer 26 include both natural and synthetic organic polymers, and mixtures thereof, such as gelatin, albumen, casein, alginates; gums such as tragacanth, and arabic; hydrolyzed mixtures of polyvinyl alcohol with its carboxylic acid esters from which the polyvinyl alcohol can be derived by hydrolysis; cellulose derivatives such as cellulose glycollic acid, carboxymethyl cellulose; water soluble or hydrophilic polycarbamides, water soluble polyamides, polyvinyl pyrrolidones, eopolymers of polyvinyl pyrrolidone and vinyl acetate, and certain other resins such as dimethyl hydantoin formaldehyde.

The polymeric materials may be formed into layer 26 by any of several methods including coating, casting, and extrusion and subsequent drying. The layer thus formed is preferably thin enough to allow a developer solution to dissolve same or permeate therethrough in a relatively short time, for instance, a matter of seconds or at the most minutes, and is therefore preferably not much thicker than one or two mil inches.

Despite the apparent incompatibility of most materials intended to provide enhancement of the speed of the silver halide with optical sensitizers, it has unexpectedly been found that certain ones of the polymeric materials of the type described in connection with layer 26 appear to be fully compatible with (i.e. do not impair and are not impaired by) known optical sensitizing dyes. Consequently, if it is desired to alter the spectral response of the medium, as to impart panchromaticity to the medium, a Wide variety of optical sensitizers may be employed for sensitizing the same surface of the silver halide to which layer or film 26 adheres. Suitable sensitizing dyes include typically cyanine dyes, carbocyanine dyes, such as 3,3-diethyloxacarbocyanine iodide, 3,3'-diethyl-2,2' oxathiacarbocyanine iodide, polycarbocyanines, dicyanines, merocyanines, and many other cyanine type dyes Whose precise composition is unknown. Additionally, other known optically sensitizing dyestuffs may be used.

Formation of optically sensitized media may be accomplished by providing an appropriate quantity of dye and incorporating same directly into the liquid polymeric material before the latter is coated onto the microcrystalline silver halide layer. In such case, layer 26 would then comprise a mixture of polymer and dye. Alternatively, the dye may be first applied to the silver halide layer as from an aqueous-alcohol solution, until suflicient quantities of the dye are appropriately adsorbed to provide the requisite optical sensitization, the medium then dried and the polymeric film forming material then applied to the optically sensitized surface of the silver halide stratum. In yet another method of applying the optical sensitizer, it isknown that many such dyes may be evaporated or sublimed without substantial decomposition under appropriate conditions of temperature and pressure. Consequently, the dye, in certain instances, may be applied to the silver halide layer in the form of its vapor which then condenses on the silver halide layer. It has been found that dyes thus evaporated must be after-treated with water, apparently to provide the proper adsorption of the dye to the rnicrocrystalline silver-halide layer, before anyoptical sensitization effect can be ascertained.

Surface developers and internal developers are well known to those in the art. In the examples which follow, however, the surface developer employed, sometimes known as Mitchells developer, was formed as follows:

Three stock solutions are prepared, preferably using triply-distilled water. These solutions are:

Grams (A) Metol 0.50 Sodium sulfite (anhydrous) 19.50 Hydroquinone in 250 cc. of water 1.87 (B) Sodium carbonate (anhydrous) 78.00 Potassium bromide in 1 liter of water 2.00 (C) Gelatin plus water to make 250 cc 1.25

Solution A decomposes with time, solution B keeps indefinitely, and solution C should be kept refrigerated to inhibit decomposition. These solutions are used in equal proportions to make the developer. They are mixed by adding 20 ml. quantities of first, solution B to solution A and then 20 ml. of solution C to the mixture of solutions A and B.

The internal developer used in the following examples, and sometimes known as modified Mitchells, is formed in the same manner, but to the mixture of A, B and C described above, there is added 3 ml. of a 1% sodium thiosulfate solution.

In all examples following, percentages of components are given by weight unless otherwise indicated.

The formation of the novel photographic medium of the invention and a process for using such medium to provide optionally positive or negative images may be demonstrated by the following illustrative examples:

Example I A coating solution was prepared from 20 grams of vinyl pyrrolidone-vinyl acetate (PVP/VA) copolymer in 70/30 ratio in 50% ethyl alcohol (available as E735 resin from Antara Chemicals, a division of General Aniline and Film Corp.) mixed with 80 grams of ethyl alcohol.

A substantially binder-free, microcrystalline silver halide medium was prepared by vacuum evaporation, as hereinbefore described, onto a support sheet of polyethylene terephthalate, and dipped into above solution to coat the silver halide stratum. After removal and allowing excess solution to drip off, the coated medium was dried at room temperature overnight.

The dried coated medium was exposed for 0.1 sec. in a densitorneter together with a control uncoated medium. When developed together in internal developer solution for 30 seconds the coated medium showed faster development and heavier densities, thus indicating sensitization enhancement.

Similar coated and uncoated exposed media of the type described were hand rubbed before development. After development the uncoated medium exhibited fog apparently due to abrasion, while the coated medium was clear, indicating the protective nature of the coating.

Similar coated and uncoated media were placed in a container at room temperature in an atmosphere comprising hydrogen sulfide provided from an aqueous solution of 13 sodium hydrosulfide. After two hours both media were removed, exposed and developed. The coated film gave a clear image, but the uncoated film showed severe fogging, again indicating the protective nature of the coating.

Example II A substantially binder-free, microcrystalline, silver ha lide medium was prepared as in Example I and coated with a solution of 10 grams of the E735 resin mixed with grams of alcohol. In comparison with a control medium, all of the results of Example I were substantially duplicated.

Example III An uncoated medium prepared according to Example I was exposed and then cut in half. One half was developed in internal developer alone, the other half being developed in a mixture of the same internal developer and 10% added E735 resin. No difference between the two halves in speed of development or density could be ascertained. It is apparent that the presence of the resin as a film over the silver halide microcrystals at the beginning of development accounts for the results shown in Examples I and II.

Example IV A coated medium prepared according to Example I was exposed and then cut in half. One half was washed with ethyl alcohol to remove the resin and both halves then treated with internal developer. The coated half developed faster and exhibited a denser image, confirming the requirement that the film or coating be present over the silver halide microcrystals during at least the beginning of the development process.

Example V A coating solution was prepared from 10 grams of the E735 resin mixed with 90 grams of ethyl alcohol and 5 grams of a 0.1% solution of Fesa Pan 640 (a photosensitizing dye believed to be a cyanine dye and available from Fesago G.m.b.H., Heidelburg, Germany) in methanol. This was coated onto a substantially binder-free microcrystalline silver bromide medium prepared as hereinbefore described by evaporation of silver bromide onto a support of polyethylene terephthalate.

' Upon exposure of the coated medium in a sensitometer through a Wrat-ten 25A filter and development in the internal developer, the medium showed marked enhancement of sensitivity over a similarly exposed medium coated with the resin solution having no dye which gave virtually no discernible image. When the medium coated with the mixed resin and dye was exposed to white light, it also exhibited superior sensitivity in comparison with a medium coated with resin without dye and similarly exposed and developed. The lack of antagonism between the resin sensitization and dye sensitization was quite unexpected.

Example VI A coated medium was prepared according to a modification of Example V in which Dynacolor XI 137A (a cyanine dye commercially available from Dynacolor Corp, N.Y.) was however substituted for Fesa Pan 640. Similarly, other coated media were prepared according to modifications of Exampel V in which the dyes employed (all in approximately 0.0 5% amounts) were pinacyanol; dicyanine A; 3,3 diethyl 2,2 oxathiocarbocyanine iodide; 3,3 diethyloxacarbocyanine iodide; and a dye known as Hx1 available from Xerox Corp., Rochester, NY. and believed to be a merocyanine dye. In all cases, the results were substantially identical to those of Example V under similar conditions of exposure and development in comparison with control media.

Example VII Other coated media were prepared according to modifications of Example V in which the grams of E735 resin in alcohol were respectively replaced by the following polymers in 100 g. quantities:

(a) 2.5% gelatin (obtained from Atlantic Gelatin division of General Foods Corp., Massachusetts) in water;

(b) partially hydrolyzed polyvinyl alcohol (sold under the trade name Elvanol Grade 5105 by E. I. du Pont de Nemours Co., Delaware) in water;

(c) 20% polyacrylamide (sold under the trade designation PAM by American Cyanamid Co., NY.) in water;

((1) 2% carboxymethylcellulose (sold by Hercules Powder Co., Delaware, under the designation (OMC) in water;

(e) 3% sodium alginate( sold under the trade-name Kelgin-LV by Kelso Co., N.Y.) in water;

(f) 5% polyvinylpyrrolidone in absolute ethyl alcohol (obtained from Antara Chemicals);

(g) dimethylhydantoin formaldehyde resin in water (sold under the designation DMHF by Glyco Chemicals, Pa.);

(h) 2% methyl cellulose in water (sold under the trade name Methocel 60 Hg by Dow Chemical Co.).

When each of the above was, in dried form, exposed for 0.1 second through a Wratten A filter and developed in internal developer, all showed enhanced red sensitivity over uncoated control media.

Example VIII Coated media prepared according to any of the preceding examples were exposed to a uniform white light exposure of about 0.1 second in a densitometer. The media were then each divided into four portions. In all cases, first portions, when developed in internal developer solution in darkness, provided negative images; second portions, when developed in surface developer solutions provided negative images; third portions, when developed in internal developer solutions in the presence of actinic illumination, yielded negative images; and the fourth portions, when developed in surface developer solutions in the presence of actinic illumination, provided direct posi tive images. In each of the foregoing, development time was approximately seconds.

Actinic illumination was provided from sources such as two side-by-side General Electric Co. watt fluorescent (daylight type) lamps at from 5 to 7 feet from the medium being developed; a 3 volt General Electric flashlight incandescent lamp at 4 inches from the developing medium; and in processing media comprising a sensitizing dye, actinic light could be provided from 100 watt incandescent bulbs screened variously with an Eastman Kodak Co. yellow safelight Wratten filter series 0A and a red safelight Wratten filter series 1A at distance of about 3 to 4 feet.

It will be apparent that the polymeric material employed as a coating in the foregoing examples must be a film-forming polymer, i.e., can be coated on from a liquid state but will form a dry or solid coat as hereinbefore described. Further, it is clear that the coating need be at least permeable and preferably soluble in the developer vehicle so that the developer solution can react with silver halide. The invention should be understood to extend to polymers which are soluble in vehicles other than Water and in such instances, solutions of developing agents in appropriate organic solvents will provide similar results. Further, other sensitizing dyes are clearly useful as well as other polymers inasmuch as it seems that interaction between dye and polymer does not inhibit the sensitizations achieved nor the selective formation of positive or negative images.

Since certain changes may be made in the above products and processes without departing from the scope of the invention herein involved it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted in an illustrative and not in a limiting sense.

What is claimed is: 1. A process for producing, optionally, direct positive or negative images, said process comprising:

exposing to radiation to form a latent image, a photosensitive medium comprising a stratum of microcrystalline, substantially binder-free, homogenous silver halide, sandwiched between a substantially inert support and a thin film of a substantially solid, organic, transparent, polymeric material permeable to a selected silver-halide developer solution;

selecting one of a surface silver halide developer solution and an internal silver halide developer solution;

permeating said film of the exposed medium with the selected developer solution under predetermined conditions of ambient actinic illumination to form thereby a visible silver image at said stratum, said image being a direct positive when said solution is said surface developer solution and actinic illumination is present, and being a negative when said solution is either of said developer solutions and ambient actinic illumination is substantially absent.

2. A process of photographically recording an image, comprising: exposing to a selected intensity pattern of actinic radiation a photographic element having a substantially binder-free stratum of silver halide microcrystals carried upon a supporting substrate and the surface of said stratum being covered with a thin, substantially solid, transparent film permeable to a silver halide developer material, to form a negative latent image of said pattern in said stratum developable either internally or on the surface of said microcrystals, and further exposing said stratum to a quantity of actinic radiation insuflicient to materially aifect the developability of said negative latent image internally of said microcrystals while treating said stratum with a surface developer to develop a positive image of said pattern.

3. A process as set forth in claim 2, wherein said stratum is about 0.1 to about 0.5 micron in thickness.

References Cited by the Examiner UNITED STATES PATENTS 2,173,480 9/1939 Jung 96-67 2,671,034 3/1954 Steinfeld 117-71 2,834,676 5/1958 Stanley et al 96-29 FOREIGN PATENTS 1,055,953 4/ 1959 Germany.

OTHER REFERENCES Nelson: Journal of Optical Society of America, vol. 46, pages 1016-9 (1956).

NORMAN G. TORCHIN, Primary Examiner. J. T. BROWN. Assistant Examiner. 

1. A PROCESS FOR PRODUCING, OPTICALLY, DIRECT POSITIVE OR NEGATIVE IMAGES, SAID PROCESS COMPRISING: EXPOSING THE RADIATION TO FORM A LATENT IMAGE, A PHOTOSENSITIVE MEDIUM COMPRISING A STRATUM OF MICROCRYSTALLINE, SUBSTANTIALLY BINDER-FREE, HOMOGENOUS SILVER HALIDE, SANDWICHED BETWEEN A SUBSTANTIALLY INERT SUPPORT AND A THIN FILM OF A SUBSTANTIALLY SOLID, ORGANIC, TRANSPARENT, POLYMERIC MATERIAL PERMEABLE TO A SELECTED SILVER-HALIDE DEVELOPER SOLUTION; SELECTING ONE OF A SURFACE SILVER HALIDE DEVELOPER SOLUTION AND AN INTERNAL SILVER HALIDE DEVELOPER SOLUTION; PERMEATING SAID FILM OF THE EXPOSED MEDIUM WITH THE SELECTED DEVELOPER SOLUTION UNDER PREDETERMINED CONDITIONS OF AMBIENT ACTINIC ILLUMINATION TO FORM THEREBY A VISIBLE SILVER IMAGE AT SAID STRATUM, SAID IMAGE BEING A DIRECT POSITIVE WHEN SAID SOLUTION IS SAID SURFACE DEVELOPER SOLUTION AND ACTINIC ILLUMINATION IS PRESENT, AND BEING A MEGATIVE WHEN SAID SOLUTION IS EITHER OF SAID DEVELOPER SOLUTIONS AND AMBIENT ACTINIC ILLUMINATION IS SUBSTANTIALLY ABSENT. 